1. Field of the Invention
This invention relates to air-cushion vehicles.
2. Description of the prior art
An air-cushion vehicle is described in U.S. Pat. No. 3,811,527 to Pont et Al comprising a platform carrying a source of pressurized air, which platform is supported, in operation, by a central air support cushion surrounded by a peripheral, partitioned, air-cushion assembly, the supply from the pressurized air source of the central cushion and of the peripheral assembly being effected through the intermediary of a distributing space formed below the platform. The distributing space is at least partly sub-divided into a plurality of sectors by partitions extending in a direction inwardly from the peripheral assembly, and means are provided for controlling differentially the air flow supplied to the various sectors.
In such a vehicle, the central cushions forming the "plenum chamber" are defined by a peripheral skirt, termed the internal peripheral skirt, and the peripheral support assembly comprises, for at least one of the distributing sectors, a series of so-called annular skirts which are contiguous and at least in part tangential to one another and to the internal skirt which they surround.
It is known that in such an assembly, the internal pressure of the central cushion remains substantially constant in the course of the movement of the vehicle, while in contrast the pressures in the annular skirts vary within large limits. Such mode of support in analogous to a spring suspension which comprises a large central spring (equivalent to the central cushion) of substantially uniform stiffness, and a plurality of peripheral springs (analogous to the annular skirts of the peripheral assembly) which will have non-uniform stiffnesses.
Research carried out by the Applicant has confirmed the basic viability of such a support system.
It is, however, apparent that two difficulties arise in the internal skirt assembly and the annular skirts of the peripheral assembly. In certain extreme operational conditions certain thermal damage to and sagging of the annular skirt can occur. Further, some vibration has been noted and even slight deformation has been observed of the annular skirts, these phenomena appearing to result from pressures arising in the interstitial spaces between the annular skirts and the internal skirt assembly.
It is an object of the present invention to overcome these disadvantages.